Physiological regulation of phosphate homeostasis

Synergistic activation of the human phosphate exporter XPR1 by KIDINS220 and inositol pyrophosphate

Inorganic phosphate (Pi) is essential for life, and its intracellular levels must be tightly regulated to avoid toxicity. XPR1, the sole known phosphate exporter, is critical for maintaining this balance. Here we report cryo-EM structures of the human XPR1-KIDINS220 complex in substrate-free closed and substrate-bound outward-open states, as well as an XPR1 mutant in a substrate-bound inward-facing state. In the presence of inositol hexaphosphate (InsP6) and phosphate, the complex adopts an outward-open conformation, with InsP6 binding the SPX domain and juxtamembrane regions, indicating active phosphate export. Without phosphate or InsP6, the complex closes, with transmembrane helix 9 blocking the outward cavity and a C-terminal loop obstructing the intracellular cavity. XPR1 alone remains closed even with phosphate and InsP6. Functional mutagenesis shows that InsP6, whose levels vary with Pi availability, works with KIDINS220 to regulate XPR1 activity. These insights into phosphate regulation may aid in developing therapies for ovarian cancer.

Dental Implants in Patients With End-Stage Renal Disease: A Case Series

PURPOSE

Chronic kidney disease (CKD), a widespread health problem marked by a gradual loss of kidney function, presents unique challenges in various aspects of patient care. As such, this case series aimed to assess the feasibility of dental implants in end-stage renal disease (ESRD) patients.

MATERIALS AND METHODS

Parathyroid hormone (PTH) levels were measured at the time of implant placement and implant uncovering. Radiographic evaluations were performed at 7, 15, 30, 90, and 180 days after implant placement and 180 days after prosthetic rehabilitation. Bone remodeling was evaluated based on the values of radiographic marginal bone loss, measured as the distance between the implant shoulder and the marginal bone levels.

RESULTS

Fifteen patients with ESRD received a total of 27 implants (5 in the maxilla and 22 in the mandible) installed in different regions, with a diameter of 3.75 mm, height of 8.5 mm, platform of 4.1 mm, and Morse taper connection. No correlation was found between PTH levels and primary implant stability (ρ = 0.04, p value = 0.860). PTH levels ranged from 105.1 to 1965 pg/mL (mean 613.51 ± 494.38 pg/mL). Only one implant did not demonstrate primary stability during surgery, the others ranged from 15  to 50 Ncm of stability. Seven implants failed during the evaluation due to varying degrees of bone loss. There was no significant effect of primary stability or PTH levels on implant loss.

CONCLUSION

Accelerated marginal bone loss within 6 months and reduced osseointegration in ESRD patients may lead to early implant loss and treatment challenges.

Nanoapatite-Loaded κ-Carrageenan/Poly(vinyl alcohol)-Based Injectable Cryogel for Hemostasis and Wound Healing

Immediate control of excessive bleeding and prevention of infections are of utmost importance in the management of wounds. Cryogels have emerged as promising materials for the rapid release of medication and achieving hemostasis. However, their quick release properties pose the challenge of exposing patients to high concentrations of drugs. In this study, hybrid nanocomposites were developed to address this issue by combining poly(vinyl alcohol) and κ-carrageenan with whitlockite nanoapatite (WNA) particles and ciprofloxacin, aiming to achieve rapid hemostasis and sustained antibacterial effects. A physically cross-linked cryogel was obtained by subjecting a blend of poly(vinyl alcohol) and κ-carrageenan to successive freezing-thawing cycles, followed by the addition of WNA. Furthermore, ciprofloxacin was introduced into the cryogel matrix for subsequent evaluation of its wound healing properties. The resulting gel system exhibited a 3D microporous structure and demonstrated excellent swelling, low cytotoxicity, and outstanding mechanical properties. These characteristics were evaluated through analytical and rheological experiments. The nanocomposite cryogel with 4% whitlockite showed extended drug release of 71.21 ± 3.5% over 21 days and antibacterial activity with a considerable growth inhibition zone (4.19 ± 3.55 cm). Experiments on a rat model demonstrated a rapid hemostasis property of cryogels within an average of 83 ± 4 s and accelerated the process of wound healing with 96.34% contraction compared to the standard, which exhibited only ∼78% after 14 days. The histopathological analysis revealed that the process of epidermal re-epithelialization took around 14 days following the skin incision. The cryogel loaded with WNAs and ciprofloxacin holds great potential for strategic utilization in wound management applications as an effective material for hemostasis and anti-infection purposes.

Intestinal and Renal Adaptations to Changes of Dietary Phosphate Concentrations in Rat

We have studied the role of the intestine, kidney, and several hormones when adapting to changes in dietary P concentration. Normal and parathyroidectomized (PTX) rats were fed pH-matched diets containing 0.1%, 0.6%, and 1.2% P concentrations. 32Pi uptake was determined in the jejunum and kidney cortex brush border membrane vesicles. Several hormone and ion concentrations were determined in the blood and urine of rats. Both jejunum and kidney cortex Pi transport was regulated with 5 d of chronic feeding of P diets in normal rats. Acute adaptation was determined by switching foods on day 6, which was only clearly observed in the kidney cortex of normal rats, with more statistical variability in the jejunum. However, no paradoxical increase of Pi uptake in the jejunum was reproduced after the acute switch to the 1.2% P diet. Pi uptake in the jejunum was parathyroid hormone (PTH)-independent, but in the kidney, the chronic adaptation was reduced, and no acute dietary adaptations were observed. The NaPi2a protein was more abundant in the PTX than the sham kidneys, but contrary to the modest or absent changes in Pi uptake adaptation, the transporter was similarly regulated by dietary P, as in the sham rats. PTH and fibroblast growth factor 23 (FGF23) were the only hormones regulated by all diet changes, even in fasting animals, which exhibited regulated Pi transport despite similar phosphatemia. Evidence of Pi appetite effects was also observed. In brief, our results show new characteristics of Pi adaptations, including a lack of correlation between Pi transport, NaPi2a expression, and PTH/FGF23 concentrations.